Drawing frame or system comprising an endless belt for conveying the fibrous material in slubbing, roving, and spinning frames



Aug. 24, 1954 J, ys R 2,686,939

DRAWING FRAME OR SYSTEM COMPRISING AN ENDLESS BELT FOR CONVEYING THE FIBROUS MATERIAL IN SLUBBING, ROVING, AND SPINNING FRAMES Filed Oct. 25, 1950 2 Sheets-Sheet 1 Fig. I

\lkil Inventor: JOHANN JACOB KEYSER Fig, 5

lllorneys 9 3 8 2. mm m m 2 R M F A m m a m Rm m E? SW Y EM KWWT Aug. 24, 1954 J J, DRAWING FRAME OR SYS BELT FOR VEYING SLUBBI CON NG, ROVING, AND

2 Sheets-Sheet 2 Filed Oct. 25, 1950 v! fvllllllllzrllilll.

Inventor: JOHANN JACOB KEYSER Atlgmevs Patented Aug. 24, 1954 DRAWING FRAME OR SYSTEM COMPRISING AN ENDLESS BELT FOR CONVEYING THE FIBROUS MATERIAL IN SLUBBING, ROV- ING, AND SPINNING FRAMES Johann Jacob Keyser, Aarau, Switzerland, assignor to Schiess Aktiengesellschaft, Dusseldorf-Oberkassel, Germany Application October 25, 1950, Serial No. 192,133

Claims priority, application Switzerland October 29, 1949 15 Claims.

The present invention relates to textile machines, and, more particularly to drafting assemblies for use in slubbing, roving and spinning machines.

In drawing frames heretofore in use, it was standard practice to provide a drafting apron for each individual spindle. aprons were materially longer than their width and were spaced from each other by a gap caused by a bearing for the driving shaft for said aprons. These aprons being small and thin and therefore unable by themselves to run evenly without sliding to one or the other side, required guiding means and, in addition thereto, also required tensioning means so that the apron would be under proper tension to effect the desired drafting. If one apron broke, whichwas the case not infrequently, it was necessary to remove from the end of the machine all aprons, to replace the said broken apron and then from the same end of the machine again to return the other aprons to their original place. It will be obvious that such a procedure is rather cumbersome and involves great loss of time and output. The above-mentioned gaps between two adjacent aprons are also disadvantageous inasmuch as broken threads easily get caught between the aprons, and furthermore the said gaps made it very hard for the operator to watch the drafting process on all aprons from one end of the machine or even from the center of the machine.

With this known arrangement, it is theoretically possible that each apron has a slightly different speed due to the fact that it is impos- It is a still further object of this invention to design each apron and the driving and return guide elements therefor so that all parts cooperating with an apron can be handled as a single unit, while these units can be handled independently of each other.

These and other objects and advantages of the invention will appear more clearly from thefl These drafting r irregular movement.

lowing specification in connection with. the accompanying drawings in which:

Figure 1 is a portion of a longitudinal view of a spinning machine with drafting field sections according to the invention.

Figure 2 is a longitudinal section through a drafting field section having a composite belt' encircling the driving and return guide elements.

Figure 3 is an end View showing a special form of the belt.

Figure 4 is an end view showing a different form of the belt.

Figure 5 is a diagrammatic and partially sectional view of two drafting field sections in accordance with the invention.

General arrangement Instead of using one small apron for each individual spindle, there is according to the present invention provided an apron which is so wide that it serves a plurality of spindles. Preferably the apron according to the present inven- 6 tion is materially wider than the distances between the axis of its driving shaft or driving roller and the axis of its return shaftor return roller. By using a wide apron it will be obvious that greater adhesion will be obtained between the apron and the rollers over which it passes and that furthermore the apron due to this materially increased adhesion will run much smoother than the heretofore used small aprons. The wider apron also reduces the possibilities of Furthermore, by arranging the aprons according to the present invention in such a manner that the apron surface will appear as an uninterrupted surface from one end of the machine to the other end thereof, the possibility of dirt or other foreign bodies affecting the movement of the apron is materially reduced and practically impossible since the increased friction between the wide apron and the rollers over which it passes is such that it will overcome any possible dirt or foreign body which might enter between said rollers and the apron. If however, for some special reasons one apron should not move at the same speed as the other apron, it is obvious that the arrangement according to the present invention materially cuts down the total possible irregularities in the movement of the aprons over the arrangement heretofore used. In other Words, assuming sixty spindles, the theoretical maximum. possibility in the heretofore known arrangements would be that there are sixty different speeds of the aprons. Using, for instance, one apron for six spindles in con formity with the present invention, the maximum theoretical possibility of different speeds of the aprons is only ten.

Another advantage of the arrangement according to the present invention consists in that the operator will now be able to watch the aprons of the entire machine much easier than heretofore possible since the eye is not disturbed by any spaces between the aprons so that the arrangement actually makes possible the construction of longer spinning machines, say, for instance, with a length of from seventeen to eighteen yards.

It may be emphasized that the present invention does not merely use a wider apron instead of a plurality of aprons. A replacement of the heretofore known small aprons by a wider apron immediately causes other problems. to be solved. Inasmuch as a materially wider apron is to be used according to the present invention, the first requirement consists in that the apron must be. materially thicker than the heretofore known small aprons since otherwise the apron would become undulated while in operation so that it would be impossible to carry out a proper drafting operation. The application of thicker aprons, however, causes another problem, namely, it now becomes impossible. to slip the aprons on the driving shaft from one; end of the machine. Also the problem of tensioning the apron now requires a special solution. Furthermore, it becomes necessary due to the width of the apron to support the apron between its driving shaft and its return shaft. These various problems have been solved by applicant in an extremely simple and ingenious manner. More specifically, applicant has sub-divided the driving shaft and all other elements cooperating with the aprons into a plurality of parts or sections and has created, so-to-speak, an apron unit which as an individual unit represents a drafting field section of the drafting field, the latter extending from one end of the machine to the other end thereof. The apron unit can selectively be inserted into the entire drafting field or removed therefrom without disturbing the position of the other aprons.

Such an arrangement makes it possible to obtain drawing frames having drafting fields as plain as a table surface which permit the working with quite a number of slubbings or rovings at a time, so that the structure given to the end product is by far more homogeneous than has been possible with the use of the conventional single apron systems of drafting.

According to the present invention, the width of the belt corresponds to the length of the belt driving rollers between their bearings. Preferably, the belt has a width which is greater than the conveying length thereof. The belt area may be composed of parallel single belts. It is advantageous to have the belt guided on the sides by the side faces of the bearings carrying the ends of its driving, supporting and return guide elements. But it is also possible for the belt to be guided by at least one of its, driving, supporting or return guide elements. Further, the belt may be positively driven by its driving roller, or the grip of the belt on its driving roller may be improved by fitting at least one of the two parts with a contact surface which has been specially roughened, fluted, formed, covered or treated otherwise to insure the safe grip required.

It is also advantageous to arrange for the return guide element to be carried within the belt. This can, for example, be accomplished in such a way that the return guide element is backed up by the supporting element of the belt. In this connection it is to be understood that the return guide element may be adjustably or flexioly mounted in relation to its supporting member. For stopping the drawing frame in the event of lap. formations within the sphere controlled by the return guide element, the latter may be so designed that it can be swung out of the plane of the belt.

The belt in accordance with the invention preferably consists of a length of tube of flexible material. It can, for example, be cut on from an endless profiled extruded tube.

As the belt in accordance with the invention extends to the full width of a drafting field section which consequently presents itself like a table, the clearness of design can be further increased, according to the invention, by selecting a belt having a color to contrast with that.

of the fibrous material being spun. If desired, the belt may be provided with a strengthening. insertion, for example of textile materials.

Structural arrangement As will be seen from Fig. 1, the drafting field, extending from one end of the machine to the other end has been sub-divided by bearing or supporting members l into a plurality of drafting field sections of the length L. In the particular structure shown in Fig. 1, each drafting fieldsection serves three spindles, and the apron I fully covers the entire area of a drafting field section so that a number of individual fibrous strands 2, resting on the belt or apron i as on a table surface, can be processed within the reach of the various drafting field sections A, B, C. The belt driving rollers or driving shaft sections 3, which laterally protrude from the aprons, are journalled in bearings 3 of the supports or hearing elements 4. Depending on the design of the machine, the belt or apron I may be smaller in width, but for reasons of a uniform guide on the driving rollers, it is in any case advisable for the face width of the belt to be at least equal to the conveying length a of the belt. The belt or apron may be a composite one, i. e. may be made up of individual belts I, I, I', connected together in any convenient manner to form a single belt entity.

In order to avoid, at any rate,-any lateral movements, hardly possible though they are due to the great width of the belt, the arrangement can be made so that the belt, as illustrated in Fig. l, is laterally guided by the side faces of the bearings 4 carrying its driving elements or shaft sec.- tions 3, its supporting elements (plate 5), and its return guide elements (roller 6 or rail 1 in Fig. 7). But provision may also be made to guide the belt by at least one of its driving elements 3, its supporting elements 5 or its return guide elements 6 and '5, respectively. Fig. 2 illustrates such a possibility. Here the individual belts I, I, I are provided with, side flanges 8, 8' which engage corresponding recesses 9, 9' formed into the driving and return guide elements 3 and 6, respectively.

Furthermore, the belt may be positively driven by the driving roller or shaft section 3, for example, by meshing teeth, as are shown in Fig. 3. In this case, both the driving roller 3 and. the return guide roller have teeth [0 which mesh with the teeth Iii formed on the underside of the belt.

To insure a safe adhesion and drive of the belt, the driving contact between the belt I and its driving element 3 may be improved by increasing the grip between them by providing a gripping surface for the zone of contact of at least one of the two parts concerned. There are several ways to achieve this. For instance, the driving roller or shaft section 3 may for this purpose be fluted, as shown in Figs. 4 and 7, or fitted with an elastic cover I I, such as rubber, as shown in Fig. 8. Roughening by knurling or chequered grooving is also feasible; If necessary, the cylindrically shaped return guide element may be formed in a similar way, as can be seen from Fig. 4. Likewise, the underside of the belt I may be similarly roughened or fiuted to increase the grip. Besides,

Figs. 3 and 4 illustrate undulations, corrugations or flutes formed on the top surface of the belt, which may be of advantage when working with particularly hard fibers.

The invention also suggests a very particular simplification of the construction of the machine by designing the belt I and the driving elements or shaft sections 3, supporting elements 5 and return guide elements 6 or 1 encircled by said belt so as to form a complete unit which can be inserted into, or removed from, the machine as a whole. This form of embodiment is illustrated in Fig. 5 showing two such units drawn apart on either side of a common bearing element or support 4.

r The belts i of two adjacent drafting fields each, together with the appurtenant driving rollers or shaft sections 3, supporting plates 5 and return guide elements 6, form self-contained aggregates which (after loosening the top parts-n0t shown-of the bearings) can be bodily placed on or removed from the bearing supports 4 which are of the belt I are split in their bearings, which implies that the driving rollers 3, possibly alsothe return guide elements 6, may be coupled and the supporting elements 5 fastened in the vertical center line of the supports 4, so that an aggregate can be separated from another simply by removing it from the respective bearings (after withdrawing the top parts). This arrangement is of importance to the operation of the machine insofar as the idle times caused by the exchange of the drafting sections can be reduced thereby down toan absolute minimum.

In order to place the arrangement shown in Fig. 5 into the drawing frame, the stepped protruding portion at each side of the table element 5 which is closest to the return guide element 6 is placed against the lower corresponding edge of the recess 5 and while holding the unit at the protruding ends of the drive shaft section 3, the

entire unit is tilted about the said edge of the recess 5' while the drive shaft section 3 is pressed outwardly. Immediately the supporting element or table 5 begins to snap into the recess 5, the driving shaft section 3 snaps into the bearing 3. By placing the upper bearing element or support,

' not shown in Fig. 5, upon the lower bearing element or support 4, the apron is held in its proper still further simplified by supporting the return guide elements 6 and 1, respectively, within the belt I rather than on the bearing supports. 4. Feasible forms of embodiment are shown on Figs. 5 to 9.

In the form as per Figs. 5 and 6, there are bolders l2 which are screwed into the supporting rail 5 and secured to it in a predetermined position by means of the nuts It. Carried by the front end of said holders are abutments 14 by means of which the return guide roller ii is backed up and kept in constant contact with the belt i. The abutments [4 are preferably designed as sliding bearings to enable the return guide roller to roll in them. By adjusting the screw bolt 52 it is possible to regulate the tension of the belt i.

Fig. 7 illustrates a similar system of supporting a rail 1 serving as a return guide element. Here the rail 1 is backed up against the holder it which latter is rotatable in relation to said rail and can be secured in its position by means of the nut.

It is, however, also possible for the return guide element to be flexibly supported against its bearing member, an example being shown in Fig. 8. In this case, holders 55 carrying abutments l4 are slidable in holes iii of the supporting or bearing member 5 against the action of springs I! so that the whole assembly is given a certain flexibility permitting the belt while operating to yield to the actual conditions of the fibrous material in process, or to any other factors affect ing the belt.

Provision can also be made for the return guide element to swing out of the belt travelling plane in the event of any irregularities, such as lap formations, occurring at the rollers (for example, the roller 23 in Fig. 6) co-operating with the belt within the sphere controlled by the return guide element. An example of this is shown in Fig. 8. In this instance, the sup porting rail is pivotally mounted on a shaft i8 which in turn may be fixed to the bearing supports 4 in the manner described. This shaft I8 serves as a pivot for the unit comprising the supporting rail 5 and the return guide element 5 so that the assembly can move in the direction of the arrow, should there be any interference with the belt from below. A similar efiect is attained by the arrangement shown in Fig. 9, but in this case it is not the supporting rail 5 which swings out of the belt travelling plane in the direction of the arrow, but only the holder is which is pivotally connected to it and is linked to the bolt 211 as at 2|.

It is obvious that the return guide elements 6 and 1, respectively, need not necessarily be backed up against the supporting rail 5, but may also be supported by any other member housed in the belt I, for example, a transverse bar or trans:

verse shaft cdnnecting adjacent bearing supports 4.

The broad-faced elastic; belt or apron according to the present invention is most suitably made from a length of tube of elastic material, such as rubber, synthetic rubber or other elastic synthetic materials, and is, placed, with a certain initial tension, on the, driving and return guide elements 3 and 6 or 7, respectively, so as to form a perfectly plain table surface in the machine. Its, manufacture is. greatly simplified if it is cut off; in lengths from an endless, profiled, extruded tube having a profile to suit individual mill requirements.

For, if the belts are made from pieces of a tube which can be produced in any length and of any cross-section by the extruding or jet moulding process, it is possible for gripping profiles, such as shown in Figs. 3 and 4,110 be formed on both the top and bottom surfaces of the belt.

The top surface of the belt can be colored to contrast with the color; of the fibrous material to be dealt with, this: being obtained either by coating or spraying it with a suitable paint or by dyeing the mass of the belt material accordingly. Thus, it is possible to; make the drafting fields appear sharply contrasting according to the color of the fibrous material in process, whereby the attendance of the machine is considerably simplified. For example, when working with white fibers, black belts may be chosen and vice versa, and when dealing with fibers of different colors, belts of complementary colors may be preferred.

In order to increase their travelling strength,

the belts l, as shown in Fig. 9, may be partly or wholly provided with strengthening insertions 22', for example, textile insertions.

The invention suggests advantages as cannot be.

obtained with the conventional narrow belt or apron systems of fiber control. fact that the formations of laps can be reduced down to a minimum, if not prevented at all by a suitable design of belt support, there is now insured an absolutely uniform guide to a number of fibrous strands during the drafting, which is contrary to the diversity experienced with the single belt or apron systems. With machines uniformly equipped throughout with broadfaced belts in accordance with the invention, the improvement extends to all the fibrous strands within the machine. Apart from the rise in quality, the handling times are also reduced wing to the fact that there are fewer yarn breakages and that stoppages of the machines for the purpose of replacing or repairing broken belts are avoided.

The invention is not confined to any particular type of machine nor to any particular system of drawing frame. It can be applied wherever it has been customary hitherto to employ narrow conveyor belts or aprons for moving or processing the fibrous material. Therefore, it is absolutely possible for existing machines to be modified and modernized by means of broadfaced belts according to the invention, and for new machines to be equipped therewith, also. The example shown in Figs. 1 and 6 refers to a five-roller drawing frame for worsted yarn in which the third roller has been removed and replaced by a fixed flat rail to give the necessary support to the belt.

The belt preferably consists. of a length of tube of rubber, synthetic rubber or any other elastic synthetic material having a thickness which will prevent it both from wearing out prematurely and suffering any damage due to Apart from the accidental overstressing. Thicknesses of from 1 to 2 millimeters have proved to be useful.

What we claim and wish to secure by Letters Patent is:

l. A machine unit for use in connection with, a drawing frame of a spinning or preparing ma-.. chine which has its drawing frame subdivided by roller stands into drawirr field sections and which, has a driving shaft that extends throughout: the length of the machine for driving a plurality Qf; endless belts and comprises a plurality of sub. stantially equal drivingshaft sections, said, unit; including an endless belt having a width nearly equalling the length of a driving shaft section,

' a return guide element of substantially the same length as the width of said last-mentioned endeless belt and encircled by said endless belt, said driving shaft section being provided with means for direct engagement with another driving shaft; section in said frame to thereb allow selective,- ly to insert said unit into or remove the same; from; said drawing frame as an entirety so as to effector interrupt rotative connection between said last-mentioned driving shaft section and said other driving shaft section, and means connected to said return guide element and arranged for engagement with a portion of the adjacent two roller stands to thereby allow pivoting said unit; about the axis defined by the line of contact of said lastmentione-d means with said two adja. cent roller stands.

2. A machine unit for use in connection with a drawing frame of a spinning or preparing machine which has a driving shaft that extends, throughout the length of the machine for driving a plurality of aprons and comprises a plurality of substantially equal driving shaft sections supported by a plurality of supporting means and adapted selectively to be drivinglyconnected with or disconnected from each other, said unit including an apron having a width nearly equalling the length of a driving shaft; section, a return guide element of substantially the same length as the width of said last-mentioned apron and encircled bysaid apron, carry-- ing means encircled by said apron and carrying said return guide element, said carrying means;

being adapted to be supported by said supports ing means, and a driving shaft section also en-. circled by said apron, said unit being selectively insertable into or removable from said drawing frame as an entirety so as to, effect or interrupt driving connection between said last-mentioned driving shaft section and the adjacent driving shaft sections in said frame while simultaneously respectively tensioning or relieving the tension of the apron pertaining to said unit.

3. A machine unit for use in connection with a. drawing frame of a spinning or preparing ma chine which has a driving shaft that extends. throughout the length of the machine for drivinga plurality of aprons and comprises a plurality of substantially equal driving shaft sections carried. by supporting members and adapted selectively to be drivingly connected with or disconnected; from each other, said unit including an apron having a width nearly equalling the length of a driving shaft section, a return guide element of substantially the same length as the width ofsaid last-mentioned apron and encircled by said last-mentioned apron, a driving shaft section encircled by said last-mentioned apron and laterally protruding therefrom, said driving shaft section and said return guide element being arranged in spaced relationship to each other, means in-.

terposed between said last-mentioned driving shaft section and said return guide element and encircled by said last-mentioned apron for sup-, porting the upper portion thereof, said interposed means being adapted ,to be rested in said supporting members, and means carried by saidinterposed means and supporting said return guide element. l K

4. A machine unit according to claim 2, which includes spring means continually urging the return guide element against the apron so as to tension the same.

5. A machine unit according to claim 3, which includes means carried by said interposed means and having said return guide element pivotally connected thereto.

6. A machine unit for use in connection with adrawing frame of a spinning or preparing machine which has a sectional driving shaft extending throughout the length of the machine and supported by a plurality of bearing means respectively forming part of a plurality of spaced supporting members, said unit including an apron having a width greater than its length and being adapted simultaneously to serve a plurality of spindles, table means encircled by said apron and adapted to be supported by two of said supporting members, a return guide element of substantially the same length as the width of said last-mentioned apron, said return guide element being encircled by said apron and being adapted to be supported by said table means, and a driving shaft section encircled by said apron and forming a section of said sectional driving shaft, said last-mentioned driving shaft section being selectively insertable into or removable from said bearing means of said supporting members.

7. A spinning or preparing machine which comprises in combination: a plurality of spindles,

a drawing field, bearing means spaced from each other so as to subdivide said drawing field into a plurality of drawing field sections of such a width that each drawing field section serves at least two spindles, a plurality of aprons, each of said aprons extending over the entire width of a drawing field section so that when all aprons are assembled the total upper apron surface of the entire drafting field forms a continuous surface interruptedby said bearing means only, and a sectional driving shaft encircled by all of said aprons, all sections of said shaft when in assembled position being in alignment with each other i and each of said shaft sections being provided with means for detachably rotatably engaging the normally adjacent section of said shaft.

8. A spinning or preparing machine which comprises in combination, a plurality of spindles, a drawing field, bearing means spaced from each other so as to subdivide said drawing field into a plurality of drawing field sections of such a width that each drawing field section serves at least two spindles, a plurality of aprons, each of said aprons extending over the entire width of a drawing field section so that said aprons in their assembled position present a continuous drafting surface interrupted by said bearing means only, and a driving shaft supported by said bearing means and normally encircled by and in engagement with all of said aprons for driving the same, said driving shaft comprising a plurality of driving shaft sections arranged in alignment with each other and each driving shaft section being provided with means for directly rotatably engaging another driving shaft section 10 and being removable from and insertable into said frame together with the respective apron as a unit.

9. A spinning or preparing machine which comprises in combination, a plurality of spindles, a drawing field, bearing means spaced from each other so as to subdivide said drawing field into a plurality of drawing field sections of such a width that each drawing field section serves a plurality of spindles, a plurality of aprons, each of said aprons extending over the entire width of a drawing field section so that said aprons in their assembled position present a continuous drafting surface interrupted by said bearing means only, and a driving shaft supported by said bearing means and normally encircled by and in engagement with all of said aprons for driving the same, said driving shaft comprising a plurality of driving shaft sections arranged in alignment with each other, each of said driving shaft sections being journalled in two adjacent bearing means and being adapted selectively to be directly connected to or disconnected from the normally adjacent driving shaft section for removing the respective apron from or inserting the same into the respective drawing field section.

10. A spinning or preparing machine which comprises in combination, a plurality of spindles, a drawing field, bearing means spaced from each other so as to subdivide said drawing field into a plurality of drawing field sections of such a width that each drawing field section serves at least two spindles, each of said bearing means being provided with a first bearing surface and with a second bearing surface, a plurality of aprons, each of said aprons extending over the entire width of a drawing field section so that said aprons in their, assembled position present a continuous drafting surface interrupted by said bearing means only, means respectively encircled by said apron for supporting the upper portion thereof, each of said last mentioned means having its ends supported by the first bearing surfaces of the two adjacent bearing means, and a sectional driving shaft supported by said bearing means and normally encircled by and in engagement with all of said aprons for driving the same, each section of said sectional driving shaft having its ends journalled in the second bearing surface of the two adjacent bearing means in detachable rotatable engagement with the normally adjacent shaft section.

11. A machine unit for use in connection with a drawing frame of a spinning or preparing machine having a sectional driving shaft and having bearing means at each roller stand for respectively supporting the shaft sections of said shaft, said unit comprising in combination, an endless belt having a width substantially equalling the distance between two adjacent roller stands, a shaft section encircled by said endless belt and laterally protruding therefrom, said shaft section being adapted to bejournalled in bearing means at two adjacent roller stands and having its end portions provided with coupling means for coupling the same to the normally adjacent driving shaft sections, reversing means encircled by said endless belt and spaced from said lastmentioned shaft section, and means connected to said reversing means and arranged for support by two adjacent roller stands.

12. A machine unit according to claim 6 which includes means operatively connected to said table means for varying the distance between said table means and said return guide element.

13. A machine unit according to claim 6, in which the apron consists of a plurality of endless belts arranged side by side and interconnected along their longitudinal edges so as to form a single integral endless belt unit.

14. A machine unit according 'to claim '6, in which the aprons are colored to contrast with the color of the fibrous material to be processed thereby.

15. A machine unit for use in connection with a drawing frame of a spinning or preparing machine which has a driving shaft that extends throughout the length of the machine for driving a plurality of endless belts and comprises a plurality of substantially equal driving shaft sections adapted selectively to be drivingly connected with or disconnected'from each other, said unit including an endless belt having a width nearly equalling the length of a driving shaft section, a driving shaft section encircled by said endless belt for arrangement in one loop thereof, said driving shaft section extending throughout the entire length of said belt, and a return guide element encircled by said belt and extending throughout the entire length of said belt for arrangement in the other loop of said belt, said unit being selectively insertable into or removable from said drawing frame as an entirety so as to effect or interrupt driving connection between said last-mentioned driving shaft section and the adjacent driving shaft sections in said frame while simultaneously respectively tensioning or relieving the tension of the endless belt per-tain' ing to said unit.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date V 461,855 Thompson Oct. 2'7, 1891 1,092,631 Casablancas Apr. '7, 1914 1,783,301 Morton Dec. 2, 1930 2,132,299 Jackson Oct. 4, 1938 2,141,219 Martin Dec. 27, 1938 2,252,531 Tarr Aug. 12, 1941 2,522,277 Knowland et al. Sept. 12, r950 2,553,456 Howell May 15, 1951 FOREIGN PATENTS Number Country Date 4,756 Great Britain of 1823 468,850 Great Britain July 14, 1 937 554,584 Great Britain 1 July 9, "191-"8 

